Test of observation skills and ability to recall details
phone/tablet(s) with 'PhotoFit Me' app
At a point unannounced during the meeting, get somebody (unknown to any of the Scouts) to come in to the meeting area and take something "valuable" (the more they can overact and make their presence known the better).
Leaders pretend not to notice and carry on with programme (say a game), then after a few minutes 'realise' that the valuable item is missing.
Scouts have to then compose a 'crime report' of what happened and make a photofit of the 'robber' (which is where the phone app comes in).
You could have a prize for the most recognisable photofit.
Maybe even have the 'robber' come back later to compare to photofits. Or even have them come back, in different clothes, with others in a crime line up and see which scouts can pick out the correct robber.
This may be better if the leaders aren't present when the theif takes the item, but this relise on knowing how the Scouts might react to the unknown person!